demand control

Since 2018, Renson has introduced a range of cloud-connected residential ventilation systems, including central and decentral mechanical extract ventilation (MEV), as well as fully mechanical systems with heat recovery (MVHR) (see Fig. 1). These systems incorporate smart control mechanisms that utilize different IAQ sensors (CO2, VOC, RH), to adjust the airflow rate(s) locally or centrally to the detected needs. The IAQ sensors are located at the control valves or at the central unit, but not within the rooms.

The common demand control approach for MVHR systems using one CO2 sensor within the ventilation unit is assessed based on a typical residential apartment situation using CONTAM models. The simulation results confirm that air flow and therefore fan electricity and ventilation losses can be reduced compared to constant flow control, in particular for higher nominal air exchange rates. However, under certain boundary conditions, e.g. unevenly occupied dwellings indoor air quality in certain rooms may suffer with this DCV strategy.  

The monitoring of a demand controlled heat recovery ventilation system with ground heat exchange in a zero-energy building in Groenlo, The Netherlands, revealed interesting practical insights.

The most efficient ventilation system would only operate on demand, when ventilation was "needed". Running the ventilation system all the time at a low flow rate, a rate sufficient to match the ASHRAE recommended 0.35 ACH is a crude control approach to an optimum system. Conditions in a house are not constant. On average, a constant flow rate ventilation system will work reasonably well and certainly is simple, but there are more energy efficient approaches, and users tend to shut down systems that run constantly.

The peak electrical demand of office building VAV systems will be reduced by about 1.2 Kw/1000 Ft2 by employing an Integrated Systems Demand Control Technology (ISDCT) sequence to reduce peak intake flow by about 56%.Supply, return, and exhaust fan energy decreases with reduced airflows and pressures; and chiller system energy is saved by reduced cooling coil loads.The ISDCT sequence continuously computes zone contaminant concentrations allowing compliance with reference standards.

This paper shows that well proved state-of-the-art technology can be utilized to keep annual average energy consumption in office buildings below 130 kWh/m2, which is well below today's average, without compromising any major functional or architectural concepts of modern design. The Norwegian building regulations, which were revised in 1997, demand calculation of energy consumption for new buildings. However, the minimum requirements to energy consumption can even be satisfied with a modest degree of insulation or high internal loads.

The air quality in a subway-train was studied to suggest optimal design criteria and operationconditions based on the ventilation demand by passengers. The C02 emitted from thepassengers was the tracer for this study. The C02 bioeffluent from a human body was firstlyquantified and used for the data analysis. Then the C02 concentration was monitored in asubway-train being operated.

In this paper a new strategy for controlling ventilation systems is described. The strategy provides fresh air at a flow rate proportional to an estimate of the rate at which occupants generate carbon dioxide. Thus, the ventilation rate is nearly proportional to the occupant density even under transient conditions. Properties of the new strategy are described, and the performance is compared to a concentration regulating strategy in a simulation. The new strategy is shown to respond faster to a change in the occupant density and to keep the concentration at or below a threshold.

A passive tracer gas technique has been used in an experimental study of the distribution of contaminants in a room with displacement ventilation. Humans are simulated by heated metallic bodies and the tracer concentration in the breathing zone (exposure) is shown to be greatly influenced by both the position of the tracer source and the air convection current around the bodies. It is shown that pollutants emitted close to a body are completely and directly transported to the upper mixed zone and not mixed into the lower zone.